As an side note, my local MC service shop said they replace with Quicksilver gear lube used in Mercrusier I/O's. They said they do this because it is designed to still provide protection in the event of water intrusion.
"This 90W gear lube features improved emulsifiers to help protect gears should water enter the gear housing and tackifiers to improve oil film adhesion to gears and internal components. Quicksilver High Performance Gear Lube includes extra proprietary additives to protect from metal-to-metal contact and excessive wear."
I've not had a problem with water intrusion so I still just use the recommended by Reliable. I seem to remember other posts where people switched to 50w and their hubs ran cooler.